1. Field of the Invention
At least one embodiment of the invention generally relates to implantable medical devices and data communication from implantable medical devices to an external device.
2. Description of the Related Art
Typically, implantable devices, in particular implantable medical devices, such as implantable therapy and/or monitoring devices including pacemakers, cardioverters and defibrillators or the like, may include data communication means to transmit data from the implantable medical device to an external device or vice versa. The data communication means, generally, may be used when the implantable medical device is implanted in the body of a mammal or when it is stored in a conductive package prior to the implantation.
A system for data communication with a medical device thus, generally, includes an implantable medical device and an external device such as a programmer or a communication device.
A typical implantable medical device comprises a battery, a monitoring and/or therapy control unit, in some cases additionally one or more therapy units such as stimulation units and a memory for storing control program and/or data sensed by the implantable medical device. If the implantable medical device is a pacemaker or an implantable cardioverter/defibrillator (ICD), generally, the therapy units comprise stimulation units for generating and delivering electric stimulation pulses to a patient's heart tissue (myocardium). Often, sensing units for sensing cardiac activity are provided. Sensing units, typically, may process electrical signals that represent electrical potentials that may be picked up via electrodes, e.g., in a heart.
Generally, in order to transmit data sensed by the implantable medical device to an external device, a telemetry unit may be provided. Typically the telemetry unit may allow a bidirectional data communication, that is, the telemetry unit may transmit and receive data wirelessly.
Limited battery capacity of an implantable medical device generally calls for energy-efficient data communication. An implantable medical device with limited battery power typically requires a low power communication scheme in order to program it and to download acquired data. With extremely low power communication, device longevity may be increased and longer communication sessions may be achieved.
Typical communication schemes or data communication by a telemetry unit may involve RF, magnetic, ultrasonic or galvanic communication. RF frequencies of ˜400 or ˜900 MHz or magnetic coupling in the 100s of kHz range typically require several mA of current to transmit and receive data. Such high current requirements are generally out of reach of devices with battery capacities of at most a few hundred mAh. Active transmission of galvanic pulses, generally, may also require several mA of current.
In addition, RF schemes typically require relatively large antennas and magnetic coupling requires large transmit and receive coils for communication. These transmission schemes, generally, also do not penetrate the body effectively and have ranges on the order of 5-10 cm. The space available in an implantable leadless pacer (iLP), for instance, typically would not allow such large coils or antennas. iLPs are generally designed to be placed within a heart chamber as opposite to conventional pacemakers, where the pacemaker itself is placed outside the heart and electrode leads extend from the pacemaker into the heart.
In view of the above, there is a need for a low-power communication scheme that does not employ RF or magnetic coupling.